Transcript of "Moles"

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K Warne

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Atomic Weights
You must be able to…
· Describe the mole as the SI unit for amount of substance
· Relate amount of substance to relative atomic mass
· Describe relationship between the mole and Avogadro’s
number
· Conceptualise the magnitude of Avogadro’s number
· Describe the relationship between molar mass and
relative molecular mass
· Calculate the molar mass of a substance given its
formula

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THE NEUTRAL ATOM
• The atom consists of a ……………. containing protons
and neutrons surrounded by a cloud of ………………….
• Atomic Number (Z)
Number of ……………. in the Nucleus (= number of
electrons in a neutral atom.)
• Mass number (A) = Number of protons + neutrons.
Notation
Z
A
X………….. Number
(smaller) ………….
…………. Number
(bigger) ………….
symbol
Neutrons =
………………………

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THE NEUTRAL ATOM
• The atom consists of a nucleus containing protons and
neutrons surrounded by a cloud of electrons.
• Atomic Number Z - Number of protons in the Nucleus =
number of electrons in a neutral atom.
• Mass number A = Number of protons + neutrons.
Notation
Z
A
XAtomic Number
(smaller) = PROTONS
Mass Number
(bigger) = P + N
symbol
Neutrons = Mass number –
Atomic Number
= A - Z

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Relative Mass Atomic
• Certain products, such as paper for example, are sold by the ream.
A ream is 500 sheets. Since it is impractical to actually count out
500 sheets, the weight (mass) of 500 sheets is determined; then each
ream is packaged according to this mass.
• Atoms are even smaller than paper, so it is not possible to actually
count them. However, it is possible to know the mass of an atom in
respect to the mass of another atom.
• The Relative mass of an object is expressed by comparing it
mathematically to the mass of another object. So the relative mass of
an orange in relation to a grapefruit is .6. The relative mass of the
grapefruit in relation to a grapefruit is 1.0.
• Atoms are compared to the lightest atom (hydrogen) which is 12 times
lighter (1/12 of the mass of) one carbon atom.
• THE RELATIVE ATOMIC MASS IS THE NUMBER OF TIMES
AN ATOM IS HEAVIER THAN 1/12 OF A C12 ATOM.

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The Mole
The mole is defined as, “the amount of ………….. with the same number of
……………………… particles as ….. grams of carbon 12”. (n used as symbol for
moles)
602 300 000 000 000 000 000 000
Six hundred and two thousand, three hundred, billion billion !
6.023x1023 particles
12.00 g
C
Symbol
(….)
Number of particles = no of moles x no. particles in a mole
Particles = ……………..

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The Mole
The mole is defined as, “the amount of matter with the same number of
elementary particles as 12 grams of carbon 12”. (n used as symbol for
moles)
602 300 000 000 000 000 000 000
Six hundred and two thousand, three hundred, billion billion !
6.023x1023 particles
12.00 g
C
Symbol (L)
Number of particles = no of moles x no. particles in a mole
Particles = n x L

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The Mole and Mass
The mole is defined in such a way that the MASS NUMBER (A) of an element
is equal to the relative atomic mass mass of one mole of the substance. (in
grams) - THE MOLAR MASS
• Eg Na = 23g/mol, water(H2O)=18g/mol
Z
A
XAtomic Number
(smaller)
Mass Number
(bigger)
protons + neutrons
Periodic Table Symbol
Relative atomic
mass
or
mass(g) of one
mole

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Relative Masses
• Relative atomic(Ar) - The mass of the atom relative to 1/12 of
the mass of a C12 atom. (Number of times heavier than…)
O - 16one atom of oxygen is 16 times heavier than 1/12 of the mass of a C12 atom,
Na - 23 one atom of sodium… , H - 1 etc.
• Formula mass (Mr) - The sum of all the atomic masses of the
atoms in a molecule.
Water H2O one molecule of water has a relative mass of
(2x(1)+16) = 18 - that is the molecular or formula mass of
water.
Mr(H2O) = 18 (Times heavier than…)

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The Mole - mass calculations
C + O2  CO2
Carbon reacts with oxygen to form carbon dioxide as shown.
If 0.12g of carbon are reacted with excess oxygen what mass of
carbon dioxide would be formed?
1. Balance the reaction
2. Work out moles of reactant(mass given).
3. Go through the equation to find out the number of moles
being formed
4. 4. Work out quantity asked for.

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Limiting reagent example
Ammonia gas is made by reacting ammonium chloride with calcium hydroxide
according to:
NH4Cl + Ca(OH)2  NH3 + CaCl2 + H2O
If 32.1 g of ammonium chloride reacts with 7.5 g calcium hydroxide in solution,
Show by calculation; which is the limiting reagent and what mass of ammonia
is produced.
1. Balance the reaction.
2. Calculate moles given (both).
3. Work through molar ratio to decide which is limiting reagent.
4. Use limiting reagent to calculate quantity asked as before.

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Limiting reagent example
Ammonia gas is made by reacting ammonium chloride with calcium hydroxide
according to:
NH4Cl + Ca(OH)2  NH3 + CaCl2 + H2O
If 32.1 g of ammonium chloride reacts with 7.5 g calcium hydroxide in solution,
Show by calculation; which is the limiting reagent and what mass of ammonia
is produced.

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Concentration - Molarity
The concentration of a solution is defined as the ………………. of
……………………… per ………………. (dm3) of ………………….
solute
solute
Final volume of
……………..
500cm3
=+
Concentration =
Amount of ……… (……….)
Volume of ………………
30g of
NaCl
C =
n
v

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Standard Solution
A standard solution is one
for which the concentration
is precisely known.
Since
c =
n(solute)/v(solvent)
= m/Mr V
• The number of moles of
solute (Mass)
• The volume of solution.
These values must be
accurately determined.
2.45g
Mass is determined
accurately using an
electronic balance.
• Possible accuracies of
0.1 - 0.0001g
KMnO4
Volume is measured
using a volumetric
flask.
• 250 cm3
• 100 cm3, 200 cm3,

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Weighing Technique
Procedure - Weighing by difference.
1. Zero scales and clean the pan.
2. Weigh the weighing container.
3. Add (approximately) the
required amount of salt. Take
care not to drop any salt onto
the pan.
4. Transfer the salt to a clean
beaker.
5. Reweigh the weighing
container.
6. Subtract the final mass of the
container from the mass of salt
and container to give the mass
of salt transferred to the beaker.
Mass is determined accurately
using an balance (electronic
or triple beam).
• Possible accuracies of 0.1 -
0.0001g
2.45g
KMnO4
Results:
Mass salt + container: …………
Final Mass container: …………
Mass salt transferred:

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Volumetric Flask
Making a standard solution.
1. Rinse a clean & dry 100 cm3 beaker with
a little distilled water.
2. Transfer the correctly weighed amount
of salt to the beaker. Ensure NO SALT
IS LOST.
3. Add 50 - 80 cm3 water the salt and stir
gently with a glass rod until all salt is
dissolved. DO NOT REMOVE THE
ROD FROM THE SOLUTION NOR
ALLOW ANY DROPS OF SOLUTION
TO ESCAPE.
4. Add ALL the solution to volumetric
flask via funnel. Ensure glass rod and
beaker are thoroughly rinsed. (Include
rinsings.)
5. Add enough solvent to bring the level up
to the mark.

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Hi -
This is a SAMPLE presentation only.
My FULL presentations, which contain a lot more more slides and other resources, are freely
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Have a look and enjoy!
WarneScience